During NDT/NDI operations, detecting or transmitting signals are sent into targeted test objects. Responding signals are received by the instrument or system of the NDT/NDI operation, back from the test objects. In many applications, the characteristics of the detecting signals involve amplitude and phase. However, the amplitude and phase of the responding signals often shift from their original detecting ones due to reasons that are not associated with the defects or thickness of the test objects. The shift in the responding signal's amplitude and phase in comparison to those of the original detecting signals can be attributed to factors including certain intrinsic properties of the circuitry of the probes used by the NDT/NDT operation, or the material of the test objects. Quantifying and compensating for this type of phase and amplitude shift have become significantly important to the inspection accuracy since the defects can be better isolated when the shift of the phase and amplitude caused by intrinsic factors are removed.
Phase and amplitude detection in NDT/NDI is typically used for measuring thickness and detecting flaws in various materials. The variations of phase and/or amplitude of the received alternating current (AC) signal from the transmit signal caused by the test piece determines the thickness or presence of a flaw in the material. A null circuit is also necessary to null out (subtract) phase and/or amplitude differences caused by elements other than the desired test piece such as the probe and electrical circuitry. Conventional NDT/NDI inspection or measurement systems employ mostly analog methods to perform phase and amplitude detection of a received electrical waveform from a detecting transducer. The mostly analog methods require many analog components which can induce higher noise levels and have higher temperature drift effects in the test system thereby creating larger errors in the inspection results.
Another typical problem associated with mostly analog versus digital methods of phase and amplitude detection is that it requires multiple components thereby increasing the cost of the inspection or measurement system and requiring a larger amount of printed circuit board area making the inspection or measurement system larger while digital methods can be compacted into a single field programmable gate array (FPGA), CPLD or other programmable digital device.
Ideally digital methods of phase and amplitude detection are desired due to the fact that they impose lower noise errors on the inspection and measurement results of the test piece while requiring less printed circuit board area creating smaller and therefore lower cost inspection or measurement systems.
To overcome the problems attributed to using traditional mostly analog circuitry to conduct the phase and amplitude difference, the present application presents a method and circuitry to use digital components to achieve phase and amplitude detection and compensation. The use of programmable digital devices provides many advantages including allowing for reprogram-ability of the circuit for field upgrades and new circuit configurations. Also disclosed in the present application is a digital null circuit which replaces a conventional analog null circuit which uses a larger number of components for finite compensation of phase and amplitude difference in the transducer and electrical circuit while the presently disclosed digital methods can give near infinite compensation.
The waveform generator and digital null circuit in the present disclosure employ, among other components, a digital waveform generator such as a direct digital synthesizer, known in the industry as a ‘DDS’. Other existing efforts have been found to use DDS components in NDT/NDI devices for measuring electrical impedance of transducers and the conductive targets. However in this disclosure, these existing methods using digital waveform generators in NDT/NDI devices are utilized either in a different manner or to resolve different problems that are not of concern to the present disclosure.
U.S. Pat. No. 6,703,843 (herein later as '843) discloses a digital eddy current proximity system for digitally measuring the proximity probes impedance correlative to displacement and position of the metallic target being monitored.
The U.S. Pat. No. 6,703,843 patent shows multiple discrete DDS devices for waveform generation and a discrete DSP for impedance measurement. This disclosure uses a single FPGA, CPLD or other programmable digital device with embedded DDS for signal generation and waveform measurement of phase and amplitude in a single device which is an improvement over using multiple discrete DDS and DSP devices.
More specifically, '843 calculates electrical impedance of the probe by determining a voltage 1 and a voltage 2 across a resistance means. However, the present disclosure calculates phase and amplitude by transmitting a high energy electrical waveform into a transducer which is coupled into the test piece and receives the electrical sine-wave from the transducer through the test piece to determine phase and amplitude differences from the original transmit waveform. Returning to the problem at issue, '843 does not provide a solution for detection of phase and amplitude differences.
The same inventor teaches in U.S. Pat. No. 6,850,077 a solution to a problem similar to that of the '843 patent and therefore does not provide a solution to the problem of the present disclosure.
Thus, given the problems attributed to the mostly analog approach and the lack of digital solution solving the subject problem herein discussed, a digital circuit and method for measuring and compensating phase and amplitude difference in electrical and acoustical signals in NDT/NDI devices is disclosed as follows.